Research Work at
International Center for Nano Technology
and Applied Adhesion

Proposal full title: High Performance Nano Adhesive Bonding of Space Durable Polymer and its Stability at Geosynchronous Earth Orbit

Principal Investigators:

	Prof. Dr. Sangeeta Jha, Department of Chemistry, Sikkim Manipal Institute of Technology (Sikkim Manipal University), Sikkim, India
	Prof. Dr. Sushabhan Choudhury, Department of Electronics and Communication Engineering, Sikkim Manipal Institute of Technology (Sikkim Manipal University), Sikkim, India

Co-Investigators (International Collaborators):

	Dr. J. A. Poulis, Director, Adhesion Institute, Faculty of Aerospace Engineering, Delft University of Technology, Delft, The Netherlands, email: j.a.poulis@tudelft.nl
	Dr. Shantanu Bhowmik, Senior Scientist, Faculty of Aerospace Engineering, Delft University of Technology, The Netherlands, email: s.bhowmik@tudelft.nl

Objective:

Work of particular relevance to this proposal has been on the enhancement of adhesion and of bond durability of high temperature resistant polymer such as Polyimide, which can follow surface treatments through low-pressure plasma, which increases wetting characteristics of the substrate surface, followed by preparation of high performance nano adhesive by dispersing Carbon Nano Fiber (CNF) in ultra high temperature resistant adhesive such as Polyimide adhesive with further modification of Polyimide Nano Adhesive Bonding under Electron Beam Irradiation. The work has been designed not only to improve adhesion characteristics but also keeping in view of its application to Geosynchronous Earth Orbit (GEO). Therefore, challenges will be taken for retention of adhesion and durability of high performance nano adhesive bonding of space durable polymer when subject to space climate, especially under high temperature, cryogenic atmosphere, high energy radiation (gamma rays, proton and neutron radiation) atmosphere and humid as well as chemical and other relevant cosmic atmospheres.

Task of the Project:

In search of long time and efficient service performance in the context of future generation of space applications especially at GEO, work of particular relevance to this project has been on the improvement of high performance polymer-polymer composite through high performance nano adhesive bonding by exposing the composite under electron beam irradiation.

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Based on these considerations, high temperature resistant space durable polymeric sheet such as Polyimide sheet, which also have excellent cryogenic properties and which can be joined with Polyimide sheet by employing ultra high temperature resistant Polyimide adhesive, with dispersing Carbon Nano Fiber (CNF) into the matrix adhesive as CNF’s are one of the strongest materials. It is expected that with the inclusion of CNF in the Polyimide adhesive, the cohesive strength, toughness and thermal properties of the adhesive will increase significantly. This is because, local stiffening due to nano fibers results in much improved load transfer at the adhesive-CNF interface. Therefore, these bonding could be highly useful in the structural fabrication in the space industry. However, these polymers in general exhibit insufficient adhesive bond strength due to their reasonably low surface energy. Thus, it is necessary to modify the surface of the polymer and surface modification essentially incorporates various polar functional groups on the polymer surface, which will help to enhance its surface energy and to improve adhesive bond strength.
Several surface modification methods are employed to modify the polymer surface, such as chemical treatments, thermal treatment, mechanical treatment, electrical treatments under (a) atmospheric pressure plasma (corona discharge), and, (b) low pressure plasma (glow discharge) and electron beam radiation treatment. Glow discharge under low-pressure plasma is a popular technique, which results in better uniformity in surface modification of the polymers (Yao et al, 1993; Liston et al, 1993, Akovali et al 1995, Bhowmik et al 1998, Dutta et al, 1995, Banik et al 1999, Bonin and Bui 2000). Moreover, it is a dry treatment method, which is better suited for industrial applications. It is now well established that the glow discharge treatment as well as electron beam radiation treatment creates physical and chemical changes such as crosslinking, formation of free radicals and oxygen functionalisation in the form of polar groups on polymer surface resulting in improvement of wetting and adhesion characteristics (Bag et al, 1999; Liston et al, 1993; Suzuki et al, 1986, Dorn et al 1990, Alexander et al 1997, Bhowmik et al 2001, Chattopadhyay et al 2001, Kettle et al 1997, Bonin et al 1998). Further, it is emphasised that in a glow discharge treatment different desired gases could be used for generating different gas plasmas and temperature of gas generally remains low. Therefore, the plasma plays a predominant role in the surface modification of polymers.

However, the most important problem in this polymer-polymer adhesive joint is, this joint will have to encounter space environments as stated earlier. Therefore, not only the adhesion in terms of bond strength but also the durability of the joint at GEO is the major concern. It has been established that different environments very often attack particularly to the polymer-adhesive interface. Moreover, high energy radiation especially gamma radiation is significantly harmful for polymeric materials and therefore, premature failure could takes place at the Polymer-adhesive interface resulting in significantly low joint strength.
In this regard, surface of high performance polymer such as Polyimide will be modified by using low-pressure plasma at various process parameters and under various desired process gases. The surface of carbon nano fibers will be modified by low-pressure plasma using nitrogen as process gas. This modification will essentially incorporate polar functional groups such as carboxyl, carbonyl etc. on the surface of carbon nano fibers, which would certainly permit better adhesion with the ultra high temperature resistant polyimide adhesive. Once the bonding with Polyimide is set and cured, the entire composite will be modified under electron beam irradiation, resulting in significant incorporation of crosslinking within the composite leading to substantial improvement of mechanical strength.              
  
In view of the above facts the surface modified Polyimide under low-pressure plasma will be characterized by contact angle and surface energy measurement so as to identify best wettability of the polymer surface. Physicochemical changes of the Polymer surface under the exposure of low-pressure plasma respectively will be characterized by various studies under optical microscope, Scanning Electron Microscope and X-ray Photoelectron Spectroscopy (XPS). Physicothermal changes of Polyimide, Polyimide Adhesive and carbon nano fiber dispersed Polyimide Adhesive will be characterized by Differential Scanning Calorimetry (DSC) and Thermo Gravimetric Analysis (TGA). Dispersion of carbon nano fiber into the matrix Polyimide adhesive will be studied by Atomic Force Microscopy (AFM). Lap shear tensile test under static and dynamic load will be carried out to identify the best adhesive joint. Durability studies of the best joint will be carried out at different environmental conditions under heating at different temperatures for specified time, cryogenic temperature, exposing the joint to humid as well as chemical climates and under intense high energy radiation especially gamma radiation as well as neutron and proton radiation related to GEO. Parallel experiments will monitor changes in the properties of the polymer and adhesive itself when subjected to these various environments. And finally, under these environmental conditions, the durability of the joints shall be correlated to the mode of failure of the joints under static and dynamic loadings and failure mechanism will also be correlated with stress distribution of the joints using software of Finite Element Method.

Programme and Methodology

The aim of the proposed project is to produce high performance nano adhesive bonds, suitable for use at GEO between high temperature resistant polymers such as Polyimide to Polyimide sheet (service temperature –250 0C to +400 0C) by using ultra high temperature resistant Polyimide adhesive, with the dispersion of Carbon Nano Fiber (CNF).

(i) Procurement of Materials
        (a) Carbon Nano Fiber (CNF)
        (b) Polyimide sheet
        (c) Ultra High Temperature Resistant Polyimide Adhesive

(ii) Studies on base Materials
        (a) Surface characterization by measuring contact angle and by estimating surface energy
        (b) Surface characterization by XPS and SIMS studies
        (c) Optical microscope studies
        (d) SEM (EDS) studies
        (e) AFM studies
        (f) DSC and TGA studies

(iii) Surface Modification
        (a) Surface modification of Carbon Nano Fiber (CNF) by low pressure plasma using nitrogen as process gases
        (b) Surface modification of polyimide by low pressure plasma under various parameters and various process gases

(iv) Surface Analysis after Modification
        (a) Surface characterization by measuring contact angle and by estimating surface energy
        (b) Surface characterization by XPS studies
        (c) Optical microscope studies
        (d) SEM (EDS) studies

(v) Dispersion of Carbon Nano Fiber (CNF) in Ultra High Temperature Resistant Polyimide Adhesive
        (a) AFM studies

(vi) Joining of Polyimide sheet with Polyimide sheet by the above High Performance Nano Adhesive
        (a) Polyimide sheet – Polyimide Adhesive – Polyimide sheet
        (b) Polyimide sheet –Nano Adhesive (Polyimide Adhesive+CNF) – Polyimide sheet

(vii) Modification of the Polymer-Polymer Nano Adhesive Bonding by Electron Beam Irradiation

(viii) Studies on Mechanical Properties of the Joints
        (a) Lap shear tensile test under static load
        (b) Lap shear tensile test under dynamic load

(ix) Fractographic Analysis of the Joints Fractures under the Static and Dynamic Loadings
        (a) XPS studies
        (b) Optical microscope studies
        (c) SEM (EDS) studies
        (d) AFM studies

(x) Characterization of Joints Interfaces before and after modification
        (a) XPS studies
        (b) Optical microscope studies
        (c) SEM (EDS) studies
        (d) AFM studies

(xi) Studies on Durability of the Best Joint obtained from the mechanical test under various Environmental Conditions
        (a) Heating at different temperatures for specified time
        (b) Cryogenic atmosphere
        (c) Humidity and chemical atmosphere
        (d) Ultraviolet and high energy radiation
        (e) Atomic oxygen atmosphere

(xii) Fractrographic Analysis of the Joints Fractured under the Static and Dynamic Loadings after exposure to above various Environmental Conditions
        (a) XPS studies
        (b) Optical microscope studies
        (f) SEM (EDS) studies
        (g) AFM studies

(xiii) Comparative Studies of Joint Strength and Fractograph of the best joint before and after above various Environmental Exposures

(xiv) Correlation of failure modes with stress distribution along the interfaces by finite element software

(xv) Analysis of results

(xvi) Preparation of publications


Relevance to Beneficiaries

Adhesive bonding has many advantages over other ways of joining materials, but its use is often restricted by temperature and environmental limitations. This project will ameliorate these limitations.

The advantages of adhesive bonds means that are widely used throughout advanced manufacturing industry. For example they are playing an increasingly important role in the manufacture of vehicles for road, rail transport and aerospace. In these areas the problems are analogous to those in space applications, although far less acute. Thus general manufacturing industry will certainly benefit from the advances made in this project.

More, broadly, the project aims to elucidate the fundamental mechanisms of adhesion in the bonds described and so will also benefit all scientists working in the field of adhesion.


Justification of Resources and Time Schedule

Sikkim Manipal Institute of Technology (SMIT) under Sikkim Manipal University (SMU), Sikkim, India has developed an international collaboration with Adhesion Institute, Faculty of Aerospace Engineering, Delft University of Technology, The Netherlands with the appropriate facilities and ethos that this implies. The two universities have also signed Memorandum of Understanding (MOU) for Ph.D and Postdoctoral Exchange Programme and SMIT (SMU) is going to establish a centre of excellence ‘International Centre for Nano Technology and Applied Adhesion’ (ICNTAA). ICNTAA of SMIT (SMU) is also going to introduce M.Tech programme on Applied Nano Technology (which is a combination Applied Adhesion and Nano Technology). Moreover, SMIT (SMU) is the host institution for 2nd Indo-SWISSBONDING International Congress in the pattern of SWISSBONDING International Congress (www.swissbonding.ch) to promoting knowledge on ‘Applied Adhesion and Nano Technology’ in India. Much of the equipment needed for the present investigation, is readily available due to the collaboration with Faculty of Aerospace Engineering, Delft University of Technology, The Netherlands. Therefore, resources are only requested to purchasing materials, Salary of one Senior Research Fellow (SRF) for three years, travel expenses for attending and presenting research articles in reputed International Conferences and collaborative visits to Faculty of Aerospace Engineering, Delft University of Technology, The Netherlands and purchasing one Atomic Force Microscope (AFM) for ICNTAA. The AFM for ICNTAA will be collective benefit for the institute, as SMIT (SMU) has already undertaken three major Ph.D projects in this area, and it will be very helpful for future M.Tech projects as and when SMIT (SMU) has clear planning to start M.Tech programme on Applied Nano Technology.

 

References
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2. Alexander, M. R., Jones, F. R. and Short, R. D., (1997), “Radio Frequency Hexamethyldisiloxane deposition: A Comparison of Plasma and Deposit Chemistry,” Plasma and Polymers, vol. 2, pp. 277-300.

3. Bag, D. S., Kumar, V. P. and Maiti, S., (1999), “Chemical Modification of LDPE Film,” Journal of Applied Polymer Science, Vol. 71, pp. 1041 – 1048.

4. Banik, I., Dutta, S. K., Chaki, T. K. and Bhowmick, A. K., (1999), “Structural Modification of Fluorocarbon Elastomer in Presence of Electron Beam Irradiation,” Polymer, Vol. 40, pp. 447-458.

5. Bonin, H. W., Bui, V. T., Pak, H, Poirier, E and Harris, H "Radiation Effects on Aluminum-Epoxy Adhesive Strength", J. of Appl. Polymer Science, Vol. 67, 37-47 (1998).

6. Bonin, H. W and Bui, V.T., "Composite Materials in Nuclear Industry: Specific Applications", Proc. 7th Annual International Conference on Composites Engineering", Denver, Colorado, U.S.A., 208 July 2000 (Invited).

7. Bhowmik. S, Ghosh, P. K and Ray. S, Surface Modification of HDPE and PP by Mechanical Polishing and DC Glow Discharge and their Adhesive Joining to Steel, Journal of Applied Polymer Science, Vol. 80 (2001) pp 1140 – 1149.

8. Bhowmik. S, Ghosh. P. K., Ray. S and Barthwal. S. K, Surface Modification of High Density Polyethylene and Polypropylene by DC Glow Discharge and Adhesive Bonding to Steel, Journal of Adhesion Science and Technology, Vol. 12 No. 11 (1998), pp. 1181-1204.

9. Chattopadhyay, S., Ghosh, R. N., Chaki, T. K. and Bhowmik, A. K., (2001), “Surface Analysis and Printability Studies on Electron Beam-Irradiated Thermoplastic Elastomeric Films from LDPE and EVA Blends, “Journal of Adhesion Science and Technology, Vol. 15, No. 3, pp. 303 – 320.

10. Dorn, L. and Wahona, W., (1990), “Adherend Surface Pretreatment of Ethylene – Propylene Terpolymer,” Welding and Cutting, Vol. 42, pp. 506 – 509.

11. Dutta, S. K., Bhowmick, A. K., Majali, A. B., Despande, R. S. and Chaki, T. K., (1996), “Electron Beam Modification of Ethylene Vinyl Acetate Copolymer using Trimethyl Propane Trimethacrylate,” Polymer, Vol. 37, No. 1, pp. 45-55.

12. Kettle, A. P., Beck, A. J., Jones, F. R. and Short, R. D., (1997), “Plasma Polymerisation for Molecular Engineering of Carbon Fiber Surfaces for Optimised Composites,” Composite Science and Technology, Vol. 57, pp. 1023 – 1032.

13. Liston, E. M., Martinu, L. and Wertheimer, M. R., (1993), “Plasma Surface Modification of Polymers for Improved Adhesion: A Critical Review,” Journal of Adhesion Science and Technology, Vol. 7, No. 10, pp. 1077 – 1089.

14. Suzuki, M., Kishida, A., Iwata, H. and Ikada, Y., (1986), “Graft Copolymerization of Acrylamide onto a Polyethylene Surface Pretreated with a Glow Discharge,” Macromolecules, Vol. 19, p. 1804.

15. Yao, Y., Liu, X. and Zhu, Y., (1993), “Surface Modification of High Density Polyethylene by Plasma Treatment,” Journal of Adhesion Science and Technology, Vol. 3, No. 3, pp. 63 – 75.